Entire scientific disciplines such as mechanics and chemistry are governed by the interactions between atoms and molecules. On surfaces, atomic-scale force and energy fields direct the behavior of many scientifically and technologically important phenomena such as corrosion, adhesion, friction, and surface catalysis. To advance our knowledge of the fundamentals governing these subjects, it would be useful to quantify force and energy interactions between the surface of interest and a probe with atomic resolution. For example, in the case of a catalytically active surface, this would allow a study of the role and effectiveness of atomic-scale surface defects as active sites, potentially making important contributions to this key field for energy research. Moreover, a study of lateral forces on the atomic scale would provide new insights regarding the atomic origins of friction, another field of intense research and technological importance.
In this thesis, we will show that the recently developed method of three-dimensional atomic force microscopy (3D-AFM), based on noncontact atomic force microscopy (NC-AFM), can be used towards achieving the goals described above. 3D-AFM measurements on the surface of graphite provide important atomic-scale clues regarding the excellent frictional properties of this solid lubricant, such as a remarkable localization of lateral forces around the hollow sites of the surface lattice, and a linear dependence of static friction values on normal forces in the attractive interaction regime. Furthermore, simultaneous NC-AFM and scanning tunneling microscopy (STM) measurements on the surface oxide layer on Cu(100) provide vastly different contrast modes that help explain some aspects of atomic-scale contrast formation mechanisms in these imaging methods, with help from ab initio density functional theory (DFT) simulations. More importantly, the combination of 3D-AFM with simultaneous STM and DFT calculations allows the quantification of the effect of surface defects on the chemical interaction forces associated with individual oxygen atoms on this sample surface, providing direct, real space proof that surface defects influence chemical reactivity on the atomic scale. Lastly, combined 3D-AFM/STM measurements performed on the prototypical metal oxide surface of TiO2(110) deliver the first atomic-scale maps of chemical interaction forces on a sample surface of catalytic importance.
|Adviser||Udo D. Schwarz|
|Subjects||Nanoscience; Nanotechnology; Materials science|
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